The invention relates to a method of connecting substrate parts, in particular the two halves of a DVD (digital versatile disc) by means of an adhesive.
In DVDs, information which is stored in the form of very small elevations and pits in the surface of one DVD half is read out through the other DVD half as well as the adhesive layer between the two halves. Since the pits are very small, slight flaws in the adhesive layer in the form of small business may impair the reproduction of the information in the pits. Even if there is only a single small bubble in the adhesive layer, the DVD has to be considered defective. There may occur small bubbles even if the substrate part (DVD half) is uniformly coated with the adhesive. It has not been entirely clarified why these small bubbles occur. The small bubbles may be gas inclusions from the ambient atmosphere which are formed when pressing the two substrate parts against each other. There is also the possibility that they are formed in the adhesive by themselves. One reason therefor could be the gas evolution of solvents of the adhesive. Preferably, an adhesive having a specific viscosity is applied to the inner region of a substrate part in the form of a thick circumferential path and is flattened during the connection with the other substrate part, wherein excess adhesive is removed preferably by rapidly rotating the substrate part, i.e., the DVD. Other methods of applying the adhesive are, for instance, uniformly spraying it onto a rotating substrate part or injecting it into two convex substrate parts. In all known methods, the aforementioned small bubbles, which are detrimental to the reproduction of the data, may occur.